When treating brain aneurysms, two isn’t always better than one

Study finds one compressed stent is sometimes more effective than two overlapping stents

By Grove Potter

“When doctors see the simulated blood flow in our models, they’re able to visualize it.”

Hui Meng, professor

Department of Mechanical and Aerospace Engineering

BUFFALO, N.Y. — The old adage about two being better than
one doesn’t necessarily apply to brain surgery.

That’s according to a study performed by University at
Buffalo engineers that used high performance computing to examine
how to best treat aneurysms.

To reduce blood flow into aneurysms, surgeons often insert a
flow diverter — tiny tubes made of weaved metal, like stents
— across the opening of an aneurysm. With the blood flow into
the aneurysm reduced, the risk of rupture is minimized.

If the opening, or neck, of an aneurysm is large, surgeons will
sometimes overlap two diverters, to increase the density of the
mesh over the opening. Another technique is to compress the
diverter to increase the mesh density and block more blood
flow.

But which technique is better?

A computational study published in January in American
Journal of Neuroradiology points to the single, compressed
diverter provided that it produces a mesh denser than the two
overlapped diverters, and that it covers at least half of the
aneurysm opening.

The research, which is ongoing, could eventually help doctors
determine the best way to treat patients suffering from
aneurysms.

“When doctors see the simulated blood flow in our models,
they’re able to visualize it. They see that they need to put
more of the dense mesh here or there to diffuse the jets (of
blood), because the jets are dangerous,” said Hui Meng, a
mechanical engineering professor at UB and lead author of the
study.

Meng, PhD, holds appointments in UB’s School of
Engineering and Applied Sciences and the Jacobs School of Medicine
and Biomedical Sciences. She is also co-director of the Toshiba
Stroke Research Center at UB.

Using UB’s supercomputer

Working with UB’s supercomputing facility, the Center for
Computational Research, Robert Damiano and Nikhil Paliwal, both PhD
candidates in Meng’s lab, used virtual models of three types
of aneurysms – fusiform (balloons out on all sides), and
medium and large saccular (balloons on one side) – and
applied engineering principles to model the pressure and speed of
blood flowing through the vessels.

The engineers modeled three different diverter treatment methods
– single non-compacted, two overlapped, and single compacted
– and ran tests to determine how they would affect blood flow
in and out of the aneurysm using computational fluid dynamics.

“We used equations from fluid mechanics to model the blood
flow, and we used structural mechanics to model the devices,”
Damiano said. “We’re working with partial differential
equations that are complex and typically unsolvable by
hand.”

These equations are converted to millions of algebraic equations
and are solved using the supercomputer. The very small size of the
mesh added to the need for massive computing power.

“The diverter mesh wires are 30 microns in
diameter,” Paliwal said. “To accurately capture the
physics, we needed to have a maximum of 10 to 15 micron grid sizes.
That’s why it is computationally very expensive.”

Compressed versus overlapped

The models showed that compressing a diverter produced a dense
mesh that covered 57 percent of a fusiform-shaped aneurysm. That
proved more effective than overlapping two diverters.

The compacted diverter was less effective in saccular aneurysms.
As diverters are compressed, they become wider and bump into the
sides of the vessel, so they could not be compressed enough to
cover a small opening of an aneurysm. Compression was more
effective in a large necked saccular aneurysm, producing a dense
mesh that covered 47 percent of the opening.

Complete coverage of an aneurysm using a solid diverter is not
favorable because a porous scaffold is needed to allow cell and
tissue growth around the neck of the aneurysm, Paliwal said. In
addition, the danger of blocking off smaller arteries prevents the
use of solid diverters.

Next, as part of a National Institutes of Health-funded project,
the team wants to look back over hundreds of previous cases, to
determine how blood flow was affected by the use of diverters. The
idea is to build a database so that more definitive conclusions can
be drawn.

“We’re going to look at and model previous cases,
and hopefully we’ll have a way to determine the best
treatment to cause the best outcome for new aneurysm cases,”
Damiano said.